Method for fabricating capacitor in semiconductor device

ABSTRACT

The present invention relates to a method for fabricating a capacitor in a semiconductor device through the use of hafnium-terbium oxide (Hf 1-x Tb x O) as a dielectric layer. The method includes the steps of: forming a lower electrode on a substrate; forming an amorphous hafnium-terbium oxide (Hf 1-x Tb x O) dielectric layer on the lower electrode; crystallizing the Hf 1-x Tb x O dielectric layer by performing a thermal process; and forming an upper electrode on the Hf 1-x Tb x O dielectric layer.

FIELD OF THE INVENTION

The present invention relates to a method for fabricating a capacitor ina semiconductor device; and, more particularly, to a method forfabricating a capacitor in a semiconductor device with use ofhafnium-terbium oxide.

DESCRIPTION OF RELATED ARTS

A recent progression in micronization in semiconductor technology hasled to acceleration in achieving a large-scale of integration of amemory device. As a result, a unit cell area is decreased and a requiredoperation voltage becomes low. Although the unit cell area is decreased,a capacitance is required to be greater than 25 fF per cell in order toprevent incidences of soft error and shortened refresh time. Therefore,there have been diverse approaches to secure a required capacitance. Forinstance, in a capacitor for use in a dynamic random access memory(DRAM) device, wherein a silicon nitride (Si₃N₄) layer formed byemploying dichlorosilane (DCS) gas is used as a dielectric layer for thecapacitor, a lower electrode is formed in three dimensions and in theform of hemisphere of which surface area is large; and a height of thecapacitor is increased.

However, the increased height of the capacitor creates a heightdifference between the cell region and the peripheral region, and thisheight difference adversely results in a difficulty in securing a depthof focus during a subsequent photo-exposure process. Hence, it islimited to have a capacitance of a capacitor required for the nextgeneration DRAM device with a memory capacitance of over 256 megabytes.

Because of this limitation, the development of the capacitor has beencurrently focused to have an appropriate height along with a sufficientcapacitance by using of a dielectric material having a high dielectricconstant. Examples of such dielectric material are tantalum oxide(Ta₂O₅) having a dielectric constant of 25, hafnium oxide (HfO₂) havinga dielectric constant ranging from 20 to 30 and alumina (Al₂O₃) having adielectric constant of 9.

Despite of the use of the high dielectric material, a Ta₂O₅ dielectriclayer is susceptible to leakage currents because the Ta₂O₅ dielectriclayer becomes deteriorated by a thermal process performed after theformation of the Ta₂O₅ layer. Also, it is limited to form an Al₂O₃dielectric layer with a sufficient capacitance because of a relativelylow dielectric constant of Al₂O₃ compared with HfO₂ and Ta₂O₅. Further,an HfO₂ dielectric layer has a low intensity of breakdown voltage,thereby being susceptible to repeated electric stress. Thus, durabilityof a capacitor with the HfO₂ dielectric layer may become reduced.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a methodfor fabricating a capacitor in a semiconductor device capable ofimproving reliability of a dielectric layer and securing a requiredcapacitance for an operation of a highly integrated device.

In accordance with an aspect of the present invention, there is provideda method for fabricating a capacitor in a semiconductor device,including the steps of: forming a lower electrode on a substrate;forming an amorphous hafnium-terbium oxide (Hf_(1-x)Tb_(x)O) dielectriclayer on the lower electrode; crystallizing the Hf_(1-x)Tb_(x)Odielectric layer by performing a thermal process; and forming an upperelectrode on the Hf_(1-x)Tb_(x)O dielectric layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome better understood with respect to the following description ofthe preferred embodiments given in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional view describing a method for fabricating acylindrical capacitor in accordance with a first embodiment of thepresent invention;

FIG. 2 is a diagram showing sequential steps of forming ahafnium-terbium oxide (Hf_(1-x)Tb_(x)O) layer, in which a subscript xrepresenting an atomic ratio of terbium (Tb), by employing an atomiclayer deposition method in accordance with the first embodiment of thepresent invention;

FIG. 3 is a cross-sectional view of a capacitor formed in the form ofconcave in accordance with a second embodiment of the present invention;and

FIG. 4 is a cross-sectional view of a capacitor in the form of innercylinder in accordance with a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A method for fabricating a capacitor in a semiconductor device inaccordance with a preferred embodiment of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view illustrating a method for fabricating acylindrical capacitor in accordance with a first embodiment of thepresent invention.

As shown, an inter-layer insulation layer 11 made of silicon dioxide(SiO₂) is formed on a semi-finished substrate 10. Although notillustrated, the semi-finished substrate 10 is provided with variousdevice elements such as transistors and bit lines by performingpredetermined processes for forming such device elements. Then, theinter-layer insulation layer 11 is etched to form contact holes 12Aexposing predetermined portions of the substrate 10. A conductivematerial is deposited into the contact holes 12A and on the inter-layerinsulation layer 11 until the contact holes 12A are filled with theconductive material. Afterwards, a chemical mechanical polishing (CMP)process or an etch-back process is performed to form contact plugs 12Bconnecting a subsequent lower electrode of a capacitor to the substrate10.

Although not illustrated, an oxide layer for forming a capacitor isformed on the above resulting substrate structure and is then etched toform holes exposing the contact plugs 12B.

Next, a metal layer or a polysilicon layer for forming a lower electrodeis formed on the holes and the oxide layer. Herein, the metal layer ismade of a material selected from a group consisting of titanium nitride(TiN), ruthenium (Ru), tantalum nitride (TaN), tungsten (W), tungstensilicide (WSi), tungsten nitride (WN), ruthenium dioxide (RuO₂), iridium(Ir), and platinum (Pt). Then, a CMP process or an etch-back process isperformed to the above metal or polysilicon layer. Thereafter, the oxidelayer is removed to form cylindrical lower electrodes 13.

In case that the lower electrodes 13 are made of polysilicon, the lowerelectrodes 13 are subjected to a cleaning process before a dielectriclayer 14 is formed for the purpose of removing a native oxide layerformed on the lower electrodes 13 and blocking hydrogen diffusions. Forthe cleaning process, hydrofluoric acid (HF) diluted with waterpreferably in a ratio of approximately 1 part of HF to approximately 10parts to approximately 100 parts of water, or a mixed solution ofdeionized water (DI) and HF that is diluted with ammonium hydroxide(NH₄OH) in a ratio of 1 part of HF to approximately 5 parts toapproximately 500 parts of NH₄OH is preferably used.

Although not illustrated, a diffusion barrier layer made of a materialselected from a family of silicon nitride (SiN_(x)) is formed on thelower electrodes 13 in order to prevent silicon or impurities from beingdiffused into a dielectric layer which will be subsequently formed. Thediffusion barrier layer is formed by nitriding a surface of the lowerelectrodes 13 through performing one of a furnace annealing process anda rapid thermal process (RTP) in an atmosphere of ammonia (NH₃) gas.

Also, before and after the above cleaning process, it is possible toperform an additional cleaning process by using a mixed solution ofammonium hydroxide (NH₄OH), hydrogen peroxide (H₂O₂) and water (H₂O), amixed solution of sulfuric acid (H₂SO₄) and H₂O₂, or a mixed solution ofH₂SO₄ and H₂O in order to remove organic or inorganic particles, orother impurities remaining on the lower electrodes 13 made ofpolysilicon.

Next, the above mentioned dielectric layer 14 is formed on the lowerelectrodes 13. At this time, the dielectric layer 14 is made ofhafnium-terbium oxide (Hf_(1-x)Tb_(x)O) and has a thickness less thanapproximately 100 Å. Herein, a subscript x represents an atomic ratio ofTb.

More specifically, the Hf_(1-x)Tb_(x)O dielectric layer 14 is formed byemploying one of an atomic layer deposition (ALD) method or a lowpressure chemical vapor deposition (LPCVD) method. At this time, such amaterial as C₁₆H₃₆HfO₄, or a precursor of Hf such an organic metalcompound as tetrakis-diethylamino-hafnium (TDEAHf) and tetrakis-ethylmethylamino-hafnium (TEMAHf) is used as a source gas of Hf. For a sourcegas of Tb, such a material as Tb(OC₂H₅)₃, or a precursor of Tb such aTb-containing organic metal compound as Tb(CH₃)₃ is used. Also, areaction gas is selected from a group consisting of O₃, O₂ plasma gasand water vapor.

In addition, since a dielectric constant of the Hf_(1-x)Tb_(x)Odielectric layer 14, a level of leakage currents and a breakdown voltagecharacteristic are determined by a Tb content, the atomic ratio of Tb,i.e., the subscript x, is set to be in a range between approximately0.03 to approximately 0.1 in order to obtain a dielectric constant ofthe Hf_(1-x)Tb_(x)O dielectric layer 14 in a range from approximately 30to approximately 50. That is, if the Hf_(1-x)Tb_(x)O dielectric layer 14having a high dielectric constant ranging from approximately 30 toapproximately 50 is formed by controlling the Tb content, it is possibleto have a thickness of an equivalent oxide layer ranging fromapproximately 10 Å to approximately 20 Å. As a result of this effect, itis further possible to secure a sufficient capacitance of a capacitor,to have a level of leakage currents lower than a hafnium oxide (HfO₂)layer and to have a pronounced breakdown voltage characteristic. Also,since the Hf_(1-x)Tb_(x)O dielectric layer 14 has a good thermalstability at a high temperature compared with the HfO₂ layer, it ispossible to prevent degradation of an electric characteristic during ahigh thermal process for crystallizing the Hf_(1-x)Tb_(x)O dielectriclayer 14, thereby improving durability and reliability of a capacitor.

Preferably, a flow rate of each of the Hf and Tb source gases iscontrolled to be in a range from approximately 50 sccm to approximately500 sccm. Meanwhile, a flow rate of the reaction gas is controlled to bein a range from approximately 0.1 slm to approximately 1 slm. In casethat O₃ is used as the reaction gas, a concentration of the O₃ reactiongas is controlled to be in a range between approximately 220 g/m³ andapproximately 180 g/m³.

If the Hf_(1-x)Tb_(x)O dielectric layer 14 is formed by employing an ALDmethod, two cycles respectively for forming a HfO₂ layer and a terbiumoxide (Tb_(x)O_(y)) layer, in which subscripts x and y represent arespective atomic ratio of Tb and O are repeatedly performed.Especially, a first cycle for forming the HfO₂ layer includes thesequential steps of providing a source gas of Hf, providing a purge gassuch as N₂ or Ar gas, providing a reaction gas of O₃, and providing apurge gas such as N₂ or Ar gas, and a second cycle for forming theTb_(x)O_(y) layer includes the sequential steps of providing a sourcegas of Tb, providing a purge gas such as N₂ or Ar gas, providing areaction gas of O₃, and providing a purge gas such as N₂ or Ar gas.Particularly, the first and the second cycles are repeated in arespective ratio less than approximately 9 to approximately 1. It isalso possible to repeatedly perform a cycle including the sequentialsteps of providing a source gas of Hf, providing a purge gas of N₂ orAr, providing a source gas of Tb, providing a purge gas of N₂ or Ar,providing a reaction gas of O₃, and providing a purge gas of N₂ or Ar.At this time, the number of providing the Hf source gas and that ofproviding the Tb source gas is set to be in a ratio less thanapproximately 9 to approximately 1.

If the LPCVD method is used to form the Hf_(1-x)Tb_(x)O dielectric layer14, inorganic metal compounds individually containing Hf and Tb arecontrolled to have a ratio of Hf and Tb less than approximately 9 toapproximately 1 through the use of a flow controller such as a mass flowcontroller (MFC) and are then vaporized by a vaporizer maintained with atemperature ranging from approximately 150° C. to approximately 300° C.Thereafter, these Hf and Tb source gases are provided to a LPCVDreaction chamber maintained with a temperature ranging fromapproximately 250° C. to approximately 500° C.

Next, the Hf_(1-x)Tb_(x)O dielectric layer 14 is crystallized by athermal process to thereby have an improved dielectric characteristic.Herein, the thermal process is one of a furnace annealing process and arapid thermal process (RTP) and proceeds under an increasing or adecreasing pressure and at a temperature ranging from approximately 500°C. to approximately 900° C. in an atmosphere of N₂, or in an atmosphereof O₂ and N₂ mixed in a ratio less than approximately 1 to approximately10. Especially, this thermal process is performed for the purpose ofremoving impurities of carbon contained in the Hf_(1-x)Tb_(x)Odielectric layer.

Afterwards, an upper electrode 15 is formed on the Hf_(1-x)Tb_(x)Odielectric layer 14 by using a metal layer selected from a groupconsisting of TiN, Ru, TaN, W, WSi, WN, RuO₂, Ir, IrO₂, and Pt, or byusing a polysilicon layer.

Although not illustrated, in case that the upper electrode 15 is made ofpolysilicon, a diffusion barrier layer made of a nitride-based materialselected from a family of SiN_(x) is formed between the upper electrode15 and the Hf_(1-x)Tb_(x)O dielectric layer 14. The diffusion barrierlayer is formed by nitriding the Hf_(1-x)Tb_(x)O dielectric layer 14through the use of the same method applied for nitriding the lowerelectrode 13. Also, although not illustrated, a buffer layer is formedon the upper electrode 15 in order to maintain structural stability tohumidity, temperature, or an electric shock. At this time, the bufferlayer is made of polysilicon or silicon nitride and has a thicknessranging from approximately 200 Å to approximately 1000 Å.

FIG. 2 is a diagram showing the above described cycles of the ALD methodfor forming a hafnium-terbium oxide (Hf_(1-x)Tb_(x)O) layer, in which asubscript x represents an atomic ratio of Tb in accordance with thefirst embodiment of the present invention. As shown, each cycle includessteps of sequentially providing a source gas, a purge gas, a reactiongas and a purge gas. More specifically, as described above, theHf_(1-x)Tb_(x)O dielectric layer 14 is formed by repeatedly performingtwo cycles respectively for forming a HfO₂ layer and a terbium oxide(Tb_(x)O_(y)) layer, in which subscripts x and y represent a respectiveatomic ratio of Tb and O. A first cycle for forming the HfO₂ layerincludes the sequential steps of providing a source gas of Hf, providinga purge gas such as N₂ or Ar gas, providing a reaction gas of O₃, andproviding a purge gas such as N₂ or Ar gas, and a second cycle forforming the Tb_(x)O_(y) layer includes the sequential steps of providinga source gas of Tb, providing a purge gas such as N₂ or Ar gas,providing a reaction gas of O₃, and providing a purge gas such as N₂ orAr gas.

Particularly, the first and the second cycles are repeated in arespective ratio less than approximately 9 to approximately 1. It isalso possible to repeatedly perform a cycle including the sequentialsteps of providing a source gas of Hf, providing a purge gas of N₂ orAr, providing a source gas of Tb, providing a purge gas of N₂ or Ar,providing a reaction gas of O₃, and providing a purge gas of N₂ or Ar.At this time, the number of providing the Hf source gas and that ofproviding the Tb source gas is set to be in a ratio less thanapproximately 9 to approximately 1.

In accordance with the first embodiment of the present invention, theHf_(1-x)Tb_(x)O layer is used as a dielectric layer of the capacitor tothereby obtain an equivalent oxide layer having a thickness (Tox)ranging from approximately 10 Å to approximately 20 Å and a highdielectric constant ranging from approximately 30 to approximately 50.As a result of this effect, it is possible to secure a sufficientcapacitance of the capacitor required for operations of a highlyintegrated device. Also, reliability of the dielectric layer can beimproved since it is possible to obtain a low level of leakage currentscompared with an HfO₂ layer and a pronounced breakdown voltagecharacteristic. Furthermore, because of a good thermal stability in ahigh temperature, it is further possible to improve durability andreliability of the capacitor.

Meanwhile, although a case of applying a hemispherical grain structureor a concavo-convex structure to the lower electrode is not exemplifiedin the first embodiment, it is still possible to maximize a surface areaof the capacitor by forming the lower electrode made of polysilicon andthen applying the HSG or concavo-convex structure to the lowerelectrode.

Also, although the first embodiment of the present invention exemplifiesa case of forming the lower electrode 13 in the form of cylinder, thefirst embodiment of the present invention can be applied to form a lowerelectrode in a concave type or an inner cylinder type.

FIG. 3 shows a case of forming the lower electrode 13A in the concavetype in accordance with a second embodiment of the present invention.Meanwhile, FIG. 4 shows a case of forming the lower electrode 13B in theinner hemispherical grain (HSG) cylinder type in accordance with a thirdembodiment of the present invention. Herein, the same reference numeralsused in the first embodiment are used for the second embodiment and thethird embodiment, and detailed description on the formation of the lowerelectrode 13A in the form of concave type and on that of the lowerelectrode 13B in the form of inner HSG cylinder type will be omitted. Itshould be noted that, unlike the cylindrical lower electrode 13 formedunder a state that the capacitor oxide layer is removed, the lowerelectrode 13A is formed in the presence of a capacitor oxide layer 11A.In the mean time, the lower electrode 13B is formed by forming HSG oninner walls of the cylindrical lower electrode.

Furthermore, the first embodiment can be identically applied to a casethat each of the lower electrode 13A formed in the cylinder type and thelower electrode 13B formed in the inner cylinder type is made ofpolysilicon to form the HSG structure or the concavo-convex structure onsurfaces of the lower electrodes 13A and 13B. The reference numeral 20in FIGS. 3 and 4 represents this HSG or concavo-convex structure.

In accordance with the first to the third preferred embodiments of thepresent invention, the dielectric layer made of Hf_(1-x)Tb_(x)O makes itpossible to improve reliability of the dielectric layer and secure asufficient capacitance of the capacitor.

The present application contains subject matter related to the Koreanpatent application No. KR 2003-0089418, filed in the Korean PatentOffice on Dec. 10, 2003, the entire contents of which being incorporatedherein by reference.

While the present invention has been described with respect to certainpreferred embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1-3. (canceled)
 4. A method for fabricating a capacitor in asemiconductor device, the method comprising the steps of: forming alower electrode on a substrate; forming an amorphous hafnium-terbiumoxide (Hf_(1-x)Tb_(x)O) dielectric layer on the lower electrode;crystallizing the Hf_(1-x)Tb_(x)O dielectric layer by performing athermal process; and forming an upper electrode on the Hf_(1-x)Tb_(x)Odielectric layer, wherein the Hf_(1-x)Tb_(x)O dielectric layer is formedwith a thickness less than approximately 100 Å and the Hf_(1-x)Tb_(x)Odielectric layer is formed by an atomic layer deposition (ALD) method.5. A method for fabricating a capacitor in a semiconductor device, themethod comprising the steps of: forming a lower electrode on asubstrate; forming an amorphous hafnium-terbium oxide (Hf_(1-x)Tb_(x)O)dielectric layer on the lower electrode; crystallizing theHf_(1-x)Tb_(x)O dielectric layer by performing a thermal process; andforming an upper electrode on the Hf_(1-x)Tb_(x)O dielectric layer,wherein the Hf_(1-x)Tb_(x)O dielectric layer is formed with a thicknessless than approximately 100 Å and the Hf_(1-x)Tb_(x)O dielectric layeris formed by a low pressure chemical vapor deposition (LPCVD) method. 6.The method of claim 4, wherein the Hf_(1-x)Tb_(x)O dielectric layer isformed by using a source gas of hafnium (Hf) selected from a groupconsisting of C₁₆H₃₆HfO₄ and Hf-precursors of Hf-containing organicmetal compounds.
 7. The method of claim 4, wherein the Hf_(1-x)Tb_(x)Odielectric layer is formed by using a source gas of Tb selected from agroup consisting of Tb(OC₂H₅)₃ and Tb-precursors of Tb-containingorganic metal compounds.
 8. The method of claim 4, wherein a reactiongas for forming the Hf_(1-x)Tb_(x)O dielectric layer is selected from agroup consisting of O₃ gas, O₂ plasma gas and water vapor.
 9. The methodof claim 6, wherein the Hf-source gas is supplied with a flow rateranging from approximately 50 sccm to approximately 500 sccm.
 10. Themethod of claim 7, wherein the Tb-source gas is supplied with a flowrate ranging from approximately 50 sccm to approximately 500 sccm. 11.The method of claim 8, wherein the reaction gas is supplied with a flowrate ranging from approximately 0.1 slm to approximately 1 slm.
 12. Themethod of claim 8, wherein if the O₃ gas is used as the reaction gas, aconcentration of the O₃ gas is set to be in a range of approximately200±20 g/m³.
 13. The method of claim 5, wherein the Hf_(1-x)Tb_(x)Odielectric layer is formed by using a source gas of hafnium (Hf)selected from a group consisting of C₁₆H₃₆HfO₄ and Hf-precursors ofHf-containing organic metal compounds.
 14. The method of claim 5,wherein the Hf_(1-x)Tb_(x)O dielectric layer is formed by using a sourcegas of Tb selected from a group consisting of Tb(OC₂H₅)₃ andTb-precursors of Tb-containing organic metal compounds.
 15. The methodof claim 5, wherein a reaction gas for forming the Hf_(1-x)Tb_(x)Odielectric layer is selected from a group consisting of O₃ gas, O₂plasma gas and water vapor.
 16. The method of claim 13, wherein theHf-source gas is supplied with a flow rate ranging from approximately 50sccm to approximately 500 sccm.
 17. The method of claim 14, wherein theTb-source gas is supplied with a flow rate ranging from approximately 50sccm to approximately 500 sccm.
 18. The method of claim 15, wherein thereaction gas is supplied with a flow rate ranging from approximately 0.1slm to approximately 1 slm.
 19. The method of claim 15, wherein if theO₃ gas is used as the reaction gas, a concentration of the O₃ gas is setto be in a range of approximately 200±20 g/m³.
 20. The method of claim4, wherein the ALD method for forming the Hf_(1-x)Tb_(x)O dielectriclayer proceeds by repeatedly performing a cycle for forming a hafniumoxide (HfO₂) layer and a cycle for forming a terbium oxide (Tb_(x)O_(y))layer, in which subscripts x and y represent atomic ratios of terbiumand oxygen, in a ratio less than approximately 9 to approximately
 1. 21.The method of claim 4, wherein the ALD method for forming theHf_(1-x)Tb_(x)O dielectric layer proceeds by repeatedly performing acycle of sequentially proving a Hf-source gas, a purge gas, a Tb sourcegas, a purge gas, a reaction gas, and a purge gas under a condition thatthe Hf source gas and the Tb source gas are provided in a ratio lessthan approximately 9 to approximately
 1. 22. The method of claim 5,wherein the LPCVD method for forming the Hf_(1-x)Tb_(x)O dielectriclayer proceeds by vaporizing organic metal compounds individuallycontaining Hf and Tb in a respective ratio less than approximately 9 toapproximately 1 through the use of a flow quantity controller andproviding individually the vaporized organic metal compounds to areaction chamber for the LPCVD method.
 23. The method of claim 22,wherein the reaction chamber for the LPCVD method is maintained with atemperature ranging from approximately 250° C. to approximately 500° C.24-28. (canceled)